Solid wastes

Three basic types of solid waste arise at nuclear power stations:

• Low? level radioactivity waste in the form of paper, fabrics, plastics glass and metals.

• Intermediate level waste as ion-exchange resins, sludges and metals.

• Intermediate level waste as fuel cladding components.

The principles of solid waste treatment are to con­centrate and contain the radioactivity by incineration of combustible material and compaction or immo­bilisation of non-combustible waste,

l ow level waste, after compaction or incineration, is disposed of at licensed sites by burial in shallow’ trenches covered with about 1 metre of soil. Typical annual disposals by this route for magnox and AGR are given by Heap and Short [8] and are shown in Table 4.8. PWR waste estimates of this type are given by Passant (91, and are shown in Table 4.9. The radio­nuclides present in the waste are a mixture of activa­tion and fission products, with cobait-60 and caesium-
137 prominent. Ion-exchange resins and sludges from water treatment are stored as slurries in steel or con­crete tanks located in concrete cells, typically 1 metre thick, which act both as radiation shields and second­ary containment should a tank begin to leak. Storage is temporary — until the waste is processed for dis­posal. In the case of steel tanks, a corrosion allowance is made in the choice of metal thickness and if mild steel is used a protective coating is applied. Concrete tanks have a lining of steel or asphaltic paint. Provision is made for chemical dosing of the slurries, if neces­sary, to minimise corrosion of the tanks. All storage facilities have leakage detection arrangements to give early warning of failure of the primary tank.

A limited disposal of sludges to sea in sealed packages has taken place. The area selected for sea disposal is subject to international agreement and is approxi­mately 600 miles from the south-eastern point of England. The packages consist of steel drums contain­ing the sludge which has been immobilised in cement. Similar packages have been designed for ion-exchange resins using a polymer matrix in place of cement.

Metallic wastes, for example valves, pipes and re­actor control machinery, are stored in concrete cells at magnox and AGR power stations. These cells have thick walls which act as radiation shields in addition to providing containment. Like the resin and sludge cells, the walls are typically 1 m thick. The design of the facilities is such as to ensure that the waste is kept dry with provision for the checking of adventi­tious water ingress and removal.

Typical arisings of magnox and AGR sludges and resins are given by Bennett D (1983) and are shown in Table 4.10. PWR resins and sludges are given by Passant [9] and shown in Table 4.11. Fuel cladding wastes arise as the result of the removal of extraneous metal cladding and supports from the fuel before it is dispatched to a reprocessing facility. Removal of this material assists in the packing of the fuel in the transport containers.

Magnox fuel cladding (magnesium/aluminium alloy) is pyrophoric in the finely divided state and requires

TBI. E 4.10

Typical annua! ansings of sludges and resins ar magnox and AGR power smltons

Sludge

Rexm

Magnox

: :iU і: TBq

!0 tir ‘ TBq

XGR

C m ‘ *

— 1 — !1V *

* Ааіч(> per m1 procjbk similar іо magnox

TBl E 4.11

Typical annual ansings of sludges and resins at PWR power stations

Sludge

Kevin

7 nr-0.3 TBq

23 mV 100 TBq

special safety precautions. Two types of storage cell have been adopted. At some power stations the waste is stored under chemically-dosed water and at other sites is stored dry. The cells are of concrete to pro­vide containment and radiation shielding. In the wet cells, forced ventilation is provided to prevent hydro­gen build-up from the air/water reactive magnox, the air being filtered before discharge. In the dry cells, temperature probes are installed to warn of pos­sible magnox overheating, the probes being coupled to alarms. Forced ventilation is again provided to remove any hydrogen.

AGR power station fuel yields steel and graphite debris, which is accumulated in dry concrete cells, providing containment and radiation shielding. This waste is not reactive and unlike magnox waste special. precautions against fire are not necessary.

Dry solid wastes have isotopic compositions related largely to neutron activation products with the radio­nuclides Co-60, Mn-54 and Fe-59 being prominent. The isotopic composition before disposal is time dependent in view of the long storage times. Ion exchange resins contain predominantly Cs-137 and sludges are often a mixture of activation products, fission products and actinides.

National policies on disposal of radioactive wastes are under review. Environmental concern over the dumping of solid radioactive waste at sea led to in­dustrial action by the transport unions in 1983. This followed a resolution calling for a voluntary suspen­sion ot sea dumping at the 1983 meeting of the London Dumping Convention (LDC), pending the comple­tion ot an LDC scientific review. As a result the government suspended sea dumping and agreed to establish an independent review of the subject in conjunction with the Trades Union Council (TUC). This review by Holliday [10] was published in late 1984 and had the principal recommendation that the

dumping of radioactive waste at the North East At­lantic dump site should not be resumed until the cur­rent international reviews, and a comparison of sea dumping with land-based alternatives, had been com­pleted. These international reviews, due for completion in 1985, are the Ad-hoc Scientific Review — tor the LDC, the Nuclear Energy Agency (NEA) Site Suita­bility review under the Organisation of Economic Co­operation and Development (OECD) and the Review of the International Atomic Energy Agency (IAEA) Definition and Recommendations for the LDC.

A Radioactive Waste Management Advisory Com­mittee (RWMAC), established by the government, is also examining issues relating to an overall policy for the management of radioactive wastes and its fifth report to government was published in 1984. RWMAC monitors the activities of the Nuclear Industry Radio­active Waste Executive (NIREX), an organisation set up in 1982 by the principal organisations that pro­duce radioactive waste to manage the disposal of most solid low level and intermediate level radioactive waste. The activities of NIREX include the identification of land sites potentially suitable for the disposal of low and intermediate level wastes and managing the sub­sequent work.

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